The conditional deletion of targeted genes using the Cre/lox system has provided an invaluable tool for understanding the functional role of specific gene products in selected cell lineages in vivo. For studies of T cell biology, mice bearing targeted alleles are typically intercrossed with transgenic mice expressing Cre driven by the Lck, CD2, or CD4 promoters. Clear functional roles of specific signaling molecules have been established using such systems in the T cell lineage. However, as these promoters are active in developing thymocytes, the most striking phenotypes have been obtained in that compartment. In addition, because thymic selection often becomes perturbed in such mutant mice, the results of studies in peripheral T cells can be difficult, or even impossible, to interpret. Using mice transgenic for the Coxsackie and adenovirus receptor (CAR) in the T cell lineage, we recently have developed a strategy for conditional deletion of genes in post- thymic T cells using a Cre adenovirus. This tool has now allowed us to explore for the first time the deletion of specific genes of interest directly in peripheral T cells. We propose to apply this technique to gain a better understanding of the role of the lipid phosphatase PTEN in T cell biology. Conditional PTEN-deficient mice on an Lck-Cre background develop autoimmunity and T cell lymphoma. We hypothesize that these phenotypes may be a result of PTEN deletion in the thymus and might not occur when PTEN is deleted in post-thymic T cells, in which case heightened T cell immunity may nonetheless be seen. In the first Specific Aim, control and PTEN-deleted T cells will be analyzed for potentiation in IL-2 production, proliferation, and survival. Effects on differentiation into effector cell subsets, and regulation of downstream signaling events, also will be investigated. In the second Specific Aim, control and PTEN-deleted T cells will be transferred in vivo to investigate the potential for autoimmunity and lymphoma development. Whether augmented immune responses to vaccination or against syngeneic tumors occurs also will be examined. Ultimately, these experiments will allow assessment of whether pharmacologic targeting of PTEN as a future potential immunopotentiating intervention is of interest for further development. PUBLIC HEALTH RELEVANCE A strategy will be explored for genetic deletion of the negative regulatory molecule PTEN directly in peripheral T cells. Whether PTEN-deleted T cells generate improved immune responses to vaccines or against tumors, without causing autoimmunity or leading to lymphoma, will be tested. If successful, the results of this project will support development of drugs to inhibit PTEN function with the ultimate aim of improving host immune responses against cancers or chronic infections.